Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.92   3.481%   $87.8761   $87.88   $87.90   $87.90  
  Purchase #2 $58.90   13.737%   $66.9911   $66.99   $67.00   $67.00  
  Purchase #3 $213.53   13.237%   $241.795   $241.80   $241.80   $241.80  
  Purchase #4 $229.38   6.382%   $244.019   $244.02   $244.00   $244.00  
  Purchase #5 $73.89   11.506%   $82.3918   $82.39   $82.40   $82.40  
  Purchase #6 $165.66   11.571%   $184.8285   $184.83   $184.85   $184.80  
  Purchase #7 $108.88   5.317%   $114.6691   $114.67   $114.65   $114.70  
  7 purchase totals = $935.16       $1,022.5706   $1,022.58   $1,022.60   $1,022.60